1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
In this specification, a semiconductor device means all types of devices which can function by utilizing semiconductor characteristics: a display device, an electro-optical device, a photoelectric conversion device, a semiconductor circuit, and an electronic appliance are all semiconductor devices.
2. Description of the Related Art
The size of a thin film transistor has been reduced for improving productivity and saving size of a semiconductor device. As the size of a thin film transistor is reduced, the structure of the thin film transistor needs to be miniaturized, so that covering with a wiring and the like is difficult. For example, reflow using aluminum is used as a technique of filling a contact hole (see Patent Document 1). When the reflow is performed using a material with a low melting point such as aluminum is used, a diffusion prevention film formed using titanium, titanium nitride, or the like needs to be formed between a semiconductor film and the material with a low melting point in order to prevent diffusion of the material with a low melting point into the semiconductor film.